Peel and seed tomatoes and set aside. Sautee the onions in extra virgin olive oil. Add garlic and continue to sautee until the onions are translucent. Cool. Meanwhile chop tomatoes and mix with the onion and garlic mixture. Season with salt and pepper. Place equal amounts of mixture on baguette slices and top with bocconcini and pesto. Bake for about 15 minutes or until cheese has melted at 350 F.